Semiconductor devices often include multiple layers of conductive, insulating, and semiconductive layers. Often, the desirable properties of such layers improve with the crystallinity of the layer. For example, the electron mobility and electron lifetime of semiconductive layers improve as the crystallinity of the layer increases. Similarly, the free electron concentration of conductive layers and the electron charge displacement and electron energy recoverability of insulative or dielectric films improve as the crystallinity of these layers increases.
For many years, attempts have been made to grow various monocrystalline oxides on compound semiconductor materials such as gallium arsenide (GaAs). For example, gadolinium oxide (Gd2O3) has been grown overlying GaAs using ultra high vacuum e-beam techniques. Although epitaxial oxide layers can be formed overlying GaAs using this technique, the films are typically of relatively poor quality and therefore can only by grown to a limited thickness. Similarly, nickel oxide (NiO) and magnesium oxide (MgO) have been epitaxially grown on GaAs, but these oxide layers tend to turn polycrystalline when grown beyond a relatively thin layer. The attempts to grow monocrystalline oxides over compound semiconductor materials have generally been unsuccessful because lattice mismatches between the host crystal and the grown oxide have caused the resulting layer of monocrystalline material to be of low crystalline quality.
If a large area thin film of high quality monocrystalline oxide material were available at low cost, a variety of semiconductor devices could advantageously be fabricated using the material, taking advantage of the superior film properties resulting from the monocrystalline structure. In particular, the dielectric, optical, magnetic, chemical, piezoelectric and similar properties of a material generally improve as the crystallinity of the material increases.
Accordingly, a need exists for a semiconductor structure that provides a high quality monocrystalline film or layer over another monocrystalline material and for a process for making such a structure.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.